The numlock is a
switch-key on your
keyboard located in the upper-left corner of the
numeric keypad, showing "Num" and an arrow pointing downwards.
The
function of the numlock is rather
archaic: it let's you switch between the numeric keypad as such or as a
cursor field (you did need that on older computers running a text-based
OS).
If the numlock is activated, an
LED above the numeric keypad
labelled "Num Lock" will
ignite.
Today, of course, noone needs this function anymore, since
GUI's use a
mouse as
pointer. So, normally, the numlock should be activated.